Microfabrication processing of titanium for biomedical devices with reduced impact on the environment

This thesis presents research on a novel method of microfabrication of titanium (Ti) biomedical devices. The aim of the work was to develop a commercial process to fabricate Ti in a more environmentally friendly manner than current chemical etching techniques. The emphasis was placed on electrolytic etching, which enables the replacement of hazardous hydrofluoric acid-based etchants that are used by necessity when using Photochemical Machining (PCM) to produce intricate features in sheet Ti on a mass scale. Titanium is inherently difficult to etch (it is designed for its corrosion-resistant attributes) and as a result, Hydrofluoric acid (HF) is used in combination with a strong and durable mask to achieve selective etching. The use of HF introduces serious health and safety implications for those working with the process. The new technique introduces the use of a “sandwich structure”, comprising anode/insulator/cathode, directly in contact with each other and placed in an electrolytic etching cell. In this technique the same photolithography process is utilised to achieve selective etching on a metal substrate as in the PCM process. However, for the electrolytic etching stage, the inter- electrode gap (IEG) is reduced significantly from a few centimetres, as usually applied in electrochemical processes, to 4 μm. The intention behind this was to improve the current distribution experienced at the anode (Ti) during subsequent electrolytic etching. The sandwich structure was developed by deposition of a photoresist S1818 and Copper (Cu) on top of Ti. Firstly, a manual sanding of the substrate was applied in order to eliminate the oxide layers which could strongly affect a final electrolytic etching. The soft- and hard-bake stages involved in the processing of the S1818 resist were optimised to produce a stress-free Ti/S1818/Cu/S1818 structure. Ultimately a pattern would be imparted onto the S1818/Cu/S1818 that would ultimately be imparted through to the Ti layer during the last stage, electrolytic etching. In order to achieve this, a Cu electroless deposition was developed as a technique to obtain a conductive film which would act as a cathode during the electrolytic etching of the target, Ti layer. The results of the electrolytic etching of the Ti sandwich structure revealed flat-base profiles of half-etched (“half-etch” is the term used to signify an etch that does not penetrate completely through the thickness of the metal sheet) micro-holes in the Ti layer. The problem of delamination of the electroless Cu, in 10 % w/v HCl electrolyte used as an etchant, was solved by electroplating a 12 μm layer of Cu on top of the 60 nm Cu electroless deposited film. Using this technique, micro-features were achieved in Ti. The half-etched micro-holes were characterised to have an overall spherical shape corresponding to the imaged pattern and a preferred flat-base profiles (typically a raised land of material arises in conventional electrolytic etching). A series of parameters were tested in order to control the process of electrolytic etching through the Ti sandwich structure by measuring etch rate, surface roughness of the etched pattern and the etch factor. The applied current densities (CD) of 10, 15, 20, and 25 A/cm2 showed proportional dissolution to the applied current. Electrolytic etching with a CD of 20 A/cm2 demonstrated a high etch rate of 40 μm/min. and a relatively low Ra of 2.8 μm, therefore, it was utilised in further experimental work. The highest etch rate of 50 μm/min. and an improved distribution of half-etched micro-holes was achieved by the introduction of 4 crocodile connectors (2 per electrode) and mechanically stirring of the electrolyte (800 rpm) while performing the electrolytic etching. The maximum etch depth of 143.9 μm was produced in Ti when the electrolytic etching was performed at the same conditions for 3 minutes. The incorporation of ultrasonic agitation to the electrolytic etching and an electrolyte temperature of 130 C resulted in a decrease of the surface roughness of the etched micro-holes to 0.5 μm. The results of the Ti sandwich structure electrolytic etching proved the concept of minimising the IEG in order to obtain a uniform Ti dissolution on a feature scale, improved control of the electrolytic dissolution over the whole area of the sample with utilisation of the lower hazard etchant at the same time

Acid-Assisted Separation of Cathodic Material from Spent Electric Vehicle Batteries for Recycling

The recycling of lithium-ion batteries presents challenges due to the complex composition of waste streams generated by current processes. Achieving higher purity levels, particularly in the reclamation of aluminium metal and transition metal black mass, is essential for improved valorisation. In this study, we propose a high-efficiency, low-energy, and environmentally friendly method using organic acids to separate cathodic black mass from the aluminium current collector. The acids selected in this study all show >86% peeling efficiency with acetic acid showing 100% peeling efficiency of black mass from the current collector. The recovered materials were subjected to X-ray diffraction, electron microscopy, and elemental analysis techniques. We show that oxalic-acid-treated material exhibited two distinct active material components with a minimal change in mass ratio compared to the untreated material. We show by elemental analysis of the leachates that the majority of critical materials were retained in the black mass and limited aluminium was leached during the process, with almost 100% of Al recovery achieved. This methodology enables the production of high-purity concentrated aluminium and critical metal feedstocks (Mn, Co, Ni, and Li) for further hydro-metallurgical processes, upcycling of the cathode material, and direct recycling. The proposed approach offers significant potential for enhancing valorization in lithium-ion battery recycling, facilitating efficient separation and optimal recovery of valuable metals

Disassembly of Li Ion cells—characterization and safety considerations of a recycling scheme

It is predicted there will be a rapid increase in the number of lithium ion batteries reaching end of life. However, recently only 5% of lithium ion batteries (LIBs) were recycled in the European Union. This paper explores why and how this can be improved by controlled dismantling, characterization and recycling. Currently, the favored disposal route for batteries is shredding of complete systems and then separation of individual fractions. This can be effective for the partial recovery of some materials, producing impure, mixed or contaminated waste streams. For an effective circular economy it would be beneficial to produce greater purity waste streams and be able to re-use (as well as recycle) some components; thus, a dismantling system could have advantages over shredding. This paper presents an alternative complete system disassembly process route for lithium ion batteries and examines the various processes required to enable material or component recovery. A schematic is presented of the entire process for all material components along with a materials recovery assay. Health and safety considerations and options for each stage of the process are also reported. This is with an aim of encouraging future battery dismantling operations

Development of experimental techniques for parameterization of multi-scale lithium-ion battery models

Presented here, is an extensive 35 parameter experimental data set of a cylindrical 21700 commercial cell (LGM50), for an electrochemical pseudo-two-dimensional (P2D) model. The experimental methodologies for tear-down and subsequent chemical, physical, electrochemical kinetics and thermodynamic analysis, and their accuracy and validity are discussed. Chemical analysis of the LGM50 cell shows that it is comprised of a NMC 811 positive electrode and bi-component Graphite-SiOx negative electrode. The thermodynamic open circuit voltages (OCV) and lithium stoichiometry in the electrode are obtained using galvanostatic intermittent titration technique (GITT) in half cell and three-electrode full cell configurations. The activation energy and exchange current coefficient through electrochemical impedance spectroscopy (EIS) measurements. Apparent diffusion coefficients are estimated using the Sand equation on the voltage transient during the current pulse; an expansion factor was applied to the bi-component negative electrode data to reflect the average change in effective surface area during lithiation. The 35 parameters are applied within a P2D model to show the fit to experimental validation LGM50 cell discharge and relaxation voltage profiles at room temperature. The accuracy and validity of the processes and the techniques in the determination of these parameters are discussed, including opportunities for further modelling and data analysis improvements

Direct Recycling of Li_xNi_0.5Mn_0.3Co_0.2O₂ from Production Scrap and End‐Of‐Life Batteries, Using Solid‐State Relithiation

Direct recycling of Li‐ion battery cathodes offers a sustainable and potentially cost‐effective alternative to conventional methods, often involving complex chemical processes and significant material losses. This study focuses on the relithiation of cathode materials from quality control reject (QCR) and end‐of‐life (EoL) Li‐ion cells to restore their physical structure, morphology, and electrochemical performance. Two NMC532/graphite pouch cells from the same manufacturer were studied. QCR cells, stored under ambient conditions, experienced corrosion and degradation before recycling, while EoL cells were cycled to the end of life. The cells were disassembled, and the cathode materials were delaminated using NaOH solution, then relithiated with LiOH at 700 °C for 15 hours in the air. Extensive characterization analyzed elemental composition, structural properties, thermal stability, and particle size distribution. Results indicated that relithiation successfully restored lithium content and improved the structural ordering and morphology of the cathode materials. The electrochemical performance of the relithiated cathodes exhibited good stability over 100 charge‐discharge cycles. The relithiated QCR samples achieved a capacity of 155.57 mAh g−1, while EoL samples reached 152.53 mAh g−1, comparable to pristine materials. This study highlights relithiation's potential to extend the lifecycle of Li‐ion cathodes, contributing to a more sustainable circular economy for battery materials

A review of current collectors for lithium-ion batteries

Lithium-ion batteries are the state-of-the-art power source for most consumer electronic devices. Current collectors are indispensable components bridging lithium-ion batteries and external circuits, greatly influencing the capacity, rate capability and long-term stability of lithium-ion batteries. Conventional current collectors, Al and Cu foils have been used since the first commercial lithium-ion battery, and over the past two decades, the thickness of these current collectors has decreased in order to increase the energy density. However to improve the performance further, alternative materials and structures, as well as specific treatments such as etching and carbon coating, have also been investigated to enhance the electrochemical stability and electrical conductivity of current collectors, for next-generation lithium-ion batteries with higher capacities and longer service lifetime. This work reviews six types of materials for current collectors, including Al, Cu, Ni, Ti, stainless steel and carbonaceous materials, and compares these materials from five aspects of electrochemical stability, electrical conductivity, mechanical property, density and sustainability. The effects of three different structures of foil, mesh and foam as well as two treatments of chemical etching and coating are also discussed. Future opportunities are highlighted at the end of this review

Benign solvents for recycling and re-use of a multi-layer battery pouch.

This article describes a process for the repair and re-use of an aluminium-containing pouch used as an outer casing for a Lithium-ion battery cell. As Lithium-ion batteries become more widespread, particularly with their increasing use in the automotive industry and in consumer electronics, recycling them is becoming an important challenge. Current recycling approaches for Li-ion batteries focus on reclamation of the high-value metals found in the electrodes. However, in order to minimise the environmental impact of the battery it would be optimal to be able to reclaim and re-use other components. Since many battery cells consist of an electrode stack held inside an outer pouch, we herein describe the structure of such a pouch and suggest methods for selectively stripping and repairing the inner layer, allowing the material to be re-used. We investigated the use of three different solvents (xylene, limonene, and 2,2,5,5-tetramethyloxolane) for the selective stripping of the polypropylene (PP) layer on the inner side of a pouch material. Each solvent was tested on both ‘pristine’ pouch material (as obtained from the manufacturer) and pouch material that had previously been part of a battery. For ‘used’ pouch material, the overall thickness of the film decreased from 150-160μm to 70-80 μm in under 1hr for all three solvents (corresponding to the removal of the PP layer), whereas for the ‘pristine’ pouch higher temperatures and longer times were required; this result is suggestive of some polymer degradation during the life of the pouch. Following the removal of the PP layer, virgin PP was subsequently added to renew the multi-layer structure

Reclaimed and Up-Cycled Cathodes for Lithium-Ion Batteries

As electric vehicles become more widely used, there is a higher demand for lithium-ion batteries (LIBs) and hence a greater incentive to find better ways to recycle these at their end-of-life (EOL). This work focuses on the process of reclamation and re-use of cathode material from LIBs. Black mass containing mixed LiMn2O4 and Ni0.8Co0.15Al0.05O2 from a Nissan Leaf pouch cell are recovered via two different recycling routes, shredding or disassembly. The waste material stream purity is compared for both processes, less aluminium and copper impurities are present in the disassembled waste stream. The reclaimed black mass is further treated to reclaim the transition metals in a salt solution, Ni, Mn, Co ratios are adjusted in order to synthesize an upcycled cathode, LiNi0.6Mn0.2Co0.2O2 via a co-precipitation method. The two reclamation processes (disassembly and shredding) are evaluated based on the purity of the reclaimed material, the performance of the remanufactured cell, and the energy required for the complete process. The electrochemical performance of recycled material is comparable to that of as-manufactured cathode material, indicating no detrimental effect of purified recycled transition metal content. This research represents an important step toward scalable approaches to the recycling of EOL cathode material in LIBs

THE ROLE OF MINERAL NUTRITION ON YIELDS AND FRUIT QUALITY IN GRAPEVINE, PEAR AND APPLE

ABSTRACT Fertilization of temperate fruit trees, such as grapevine ( Vitis spp.), apple ( Malus domestica), and pear ( Pyrus communis) is an important tool to achive maximum yield and fruit quality. Fertilizers are provided when soil fertility does not allow trees to express their genetic potential, and time and rate of application should be scheduled to promote fruit quality. Grapevine berries, must and wine quality are affected principally by N, that regulate the synthesis of some important compounds, such as anthocyanins, which are responsible for coloring of the must and the wine. Fermenation of the must may stop in grapes with low concentration of N because N is requested in high amount by yeasts. An N excess may increase the pulp to peel ratio, diluting the concentration of anthocyanins and promoting the migration of anthocyanins from berries to the growing plant organs; a decrease of grape juice soluble solid concentration is also expected because of an increase in vegetative growth. Potassium is also important for wine quality contributing to adequate berry maturation, concentration of sugars, synthesis of phenols and the regulation of pH and acidity. In apple and pear, Ca and K are important for fruit quality and storage. Potassium is the most important component of fruit, however, any excess should be avoided and an adequate K:Ca balance should be achieved. Adequate concentration of Ca in the fruit prevents pre- and post-harvest fruit disorders and, at the same time, increases tolerance to pathogens. Although N promotes adequate growth soil N availability should be monitored to avoid excessive N uptake that may decrease fruit skin color and storability